Secretary of State Hillary Clinton checks her mobile phone after her address to the Security Council at United Nations headquarters in March 2012. Mrs. Clinton's official State Department calendar omitted or scrubbed details from at least 75 meetings she had from 2009 to 2013, an Associated Press report reveals.

As the United States moves toward the November presidential election, will voters be concerned about candidates' transparency?

That's a central question raised by an Associated Press review of Hillary Clinton's official State Department calendars. The AP found that at least 75 events were omitted or had identifying details scrubbed during her four-year tenure as Secretary of State from 2009 to 2013.

The omissions didn't violate any known federal laws, and some omissions could be the result of Mrs. Clinton's changing schedule, the AP reports. Previously, the wire service revealed in November that Clinton met or spoke by phone with nearly 100 corporate executives, donors to her charity – the Clinton Foundation – and political supporters while she was secretary of State.

But transparency around her ties to Wall Street has long been a delicate issue for the presidential candidate, one seized on frequently by Sen. Bernie Sanders (I) of Vermont during the presidential primary.

A Wall Street Journal/NBC News poll in mid-May found that Republican rival Donald Trump outpaced her by 21 percentage points, in respondents' opinions, when it came to "dealing with Wall Street." Clinton, however, was ahead on "looking out for the middle class."

The missing calendar records could also point to a longer-running issue about distinctions between public and private records that ran through debates over Clinton's use of a private email server as Secretary of State.

"It's clear that any outside influence needs to be clearly identified in some way to at least guarantee transparency. That didn't happen," Danielle Brian, executive director of the Project on Government Oversight, a nonpartisan government reform group, told the AP. "These discrepancies are striking because of her possible interest at the time in running for the presidency."

The report isn't the first time government calendars have bedeviled a public official. Former Treasury Secretary Timothy Geithner repeatedly met with officials from the bank Citigroup when he was head of the New York Federal Reserve in 2007 and 2008, an analysis by the Washington Post and ProPublica revealed in 2009.

At the time, he defended the meetings as a "routine" part of his job. But whistleblowers later raised concerns about the close relationship between New York Fed officials and another bank, Goldman Sachs.

The Treasury Department now says it redacts information from the secretary's public calendar online about sensitive financial disclosures, "internal deliberative communications," and personal information, including calls to friends and family.

But for Clinton, the decision to scrub the meetings seems to point to a long-running approach. As Secretary of State, she wrote that she sought to eliminate "any risk of the personal being accessible" in an email to a top staffer.

That message was cited in a report last month by the State Department's Inspector General that harshly criticized Clinton's email practices.

The AP reveals that Clinton's official calendar listed meetings with 124 business leaders and political donors, but not with 114 others that were identified by reviewing the planning schedule kept by her staff, which featured more details.

Clinton spokesman Nick Merrill defended the decision to omit information from the calendar, telling the AP the information in her planning schedules "simply reflect a more detailed version in one version as compared to another, all maintained by her staff."

Steven Aftergood, a government records expert at the Federation of American Scientists, told the wire service the information "wasn't necessarily a sign of bad faith." But he added, "it's obviously more important to have a complete record than a scattershot one."